Method for insulating a magnet wire with tetraalkyl titanate modified nylon

ABSTRACT

A magnet wire enamel having improved runnability and insulating properties is described comprising nylon containing 0.5% to 3.5% by weight tetraalkyl titanate. The nylon can be a sole coat, outermost coating, or bond coat.

DESCRIPTION

This is a division of copending application Ser. No. 732,534 filed onMay 10, 1985, now U.S. Pat. No. 4,599,387.

TECHNICAL FIELD

The field of art to which this invention pertains is polyamide coatingcompositions, and particularly nylon coating compositions on insulatedmagnet wire substrates.

BACKGROUND ART

Because of their relative low cost and the desirable handling propertiesthey provide to polymer insulated magnet wire, nylon topcoats have beenused in the magnet wire area for several years. However, such coatingsare not without problems. For example, on high temperature wire such asmagnet wire coated with polyester base coats, nylon overcoats havesuffered from such things as ring cracks (circular cracks perpendicularto the major axis of the coated wire) particularly in dry weather andsuch cracks can cause catastrophic wire failure. Furthermore, because ofthe relatively low solidification point of nylon, temperature changescan cause great difficulty in providing a smooth coating on wire. Partof this problem results from the fact that when applying plural coatingsof the nylon, successive coats redissolve previously applied coats, thusproducing smoothness problems.

Accordingly, what is needed in this art is a nylon composition whichovercomes such problems.

DISCLOSURE OF INVENTION

The present invention is directed to an improved magnet wire enamelcomposition comprising nylon modified by reaction with a tetraalkyltitanate. The tetraalkyl titanate reacts with the amine and carboxylgroups on the nylon molecule resulting in a nylon modified dimer withboth improved application to magnet wire substrates and improved wireproperties after application to the magnet wire substrates. Thetetraalkyl titanates are typically reacted into the nylon in an amountof about 0.25 to about 10% by weight of the nylon present in the enamelcomposition.

Another aspect of the invention is electrically insulated magnet wirecontaining a plurality of polymer layers of insulation where at leastone of the layers comprises the above-described nylon enamel.

Another aspect of the invention comprises a method of forming polymerinsulated magnet wire having a plurality of polymeric insulating layerswhere at least one of the layers is the nylon material described above.

These and other advantages of the present invention will become moreapparent from the following description.

BEST MODE FOR CARRYING OUT THE INVENTION

Any nylon material can be catalyzed with the titanate described herein.Typically nylon 6; nylon 11; nylon 6,6; nylon 6,12; etc. are used.

The tetraalkyl titanate used has the formula (RO)₄ Ti where R is analkyl group typically containing at least three carbon atoms. Preferredalkyl titanates are tetrabutyl titanate, tetrakis (2-ethylhexyl)titanate and tetraisopropyl titanate. Typically the nylon layer is usedas an overcoat on such things as standard polyester (such as THEICpolyester), polyurethane or polyvinyl formal resins. However, it canalso be used in conventional constructions as an intermediate layer(bond coat) between multiple layers of, e.g. polyurethane or as a solecoat.

Although not wishing to be bound by any particular theory it is believedthat the alkyl titanate-nylon reaction occurs as follows: ##STR1## where##STR2## represents the nylon moiety. This new molecule ##STR3## is verystable because bonding two carboxyl ##STR4## groups to a titanium centeruses up all the coordination sites on the titanium. ##STR5##

This molecule, which we will refer to as a nylon dimer, has a chemistryof its own when applied to the wire substrate. For example, when appliedto a previously applied base coat such as an hydroxyl rich polyester asdiscussed above, the following reactions take place: ##STR6## The basecoat surface is hydroxyl rich and can react with one or two of theremaining butoxy groups on the titanium nylon dimer. The above equationis written for the reaction of two alkoxy groups.

In a sole nylon coat or in the body of the film which does not interactwith other layers the following reaction takes place: ##STR7## where theO on the Ti reacts with available ##STR8##

While the polymers according to the present invention can be used on anyelectrical conductor they are preferably used on wires and specificallyon magnet wires. The wires are generally copper or aluminum and rangeanywhere from 4 AWG to 42 AWG (American Wire Gauge) in diameter, with 18AWG being the most commonly coated wire. Wire coatings can be anywherefrom 0.1 to 5 mils or any thickness desired and preferably about 3.2mils on 18 AWG wire. As stated above the coatings can be used as part ofa multicoat system in combination with conventional polymer insulationsuch as polyesters, polyurethanes, polyvinyl formal, polyimides,polyamideimides, etc. and combinations thereof. The polymer coatings canalso contain lubricants either externally on the nylon or admixed withthe nylon.

Typical multicoat systems include such things as THEIC polyester basecoats with nylon topcoats with the nylon comprising about 20 to about25% of the total thickness. When used as a bond coat, i.e. anintermediate layer between two additional layers of polymer insulation(such as a polyurethane base coat, the nylon bond coat, and a polyvinylbutyral topcoat, i.e. a solderable composition) the nylon typicallyrepresents about 5% to about 10% of the total wire product.

The enamels according to the present invention can be applied by anyconventional means such as coating dyes, roller or felt application withviscosity adjustments made accordingly. Viscosity adjustments can bemade by dilution with appropriate enamel solvents or diluents. Suchsolvents are typically cresylic acids, and methyl pyrrolidone,N,N-dimethyl or N,N-diethyl formamide and N,N-diethyl acetamide, alongwith any conventional hydrocarbon diluents such as xylene, Solvesso 100(Exxon) or D59 hydrocarbon (Drake Petroleum Company).

Conventional ovens can be used to heat treat the magnet wire afterapplication of the nylon. Typical inlet oven temperatures are of theorder of 500° F. to 700° F., preferably about 580° F. and outlet oventemperatures of about 800° F. to 1100° F., and preferably about 900° F.are used for drying and curing.

In order to demonstrate the improved and unexpected properties of nylonmodified with the tetraalkyl titanate according to the presentinvention, a series of experiments were run to ascertain the effects ofvarious additives on the enamel. A series of experiments were carriedout wherein the parts per hundred by weight (phr) of tetrabutyl titanate(TBT) in the enamel was varied from 0.05 to 1.0.

The following tables show the properties of wire made from TBT modifiedscrap nylon at a series of TBT concentrations.

These enamels were tested on 18 AWG copper with THEIC polyester basecoat in a Df (250°) range varying from 0.08 to 0.17.

    ______________________________________                                        Mandred Pull                                                                             NT*       NT     NT     13   16                                    phr TBT    0         .05    .1     .5   1.0                                   Heat Shock NT        NT     OK     OK   OK                                    phr TBT    0         .05    .1     .5   1.0                                   Runnability                                                                              8         8      81/2   -9   -9                                    phr TBT    0         .05    .1     .5   1.0                                   Flex       NT        NT     NT     OK   OK                                    phr TBT    0         .05    .1     .5   1.0                                   ______________________________________                                         *not tested  failure obvious                                             

As can readily be seen from the tables the improvement in nylon occurswhen 0.5% TBT is used. This corresponds to a 1:1 molar equivalency ofnylon to TBT.

In order to determine whether this effect would occur with virgin nylon,a virgin Vydyne® (Monsanto) 21 enamel (nylon 6,6) was run against amodified sample of the same enamel to the first failure of either, againusing THEIC polyester as base coat and 18 AWG wire construction.

    ______________________________________                                                    Mandrel  Heat    Snap/ Df                                                Tg   Pull     Shock   Flex  (250°)                                                                       Speed                                ______________________________________                                        Modified 435    18       OK    OK    .06   45                                 Virgin                                                                        Vydyne 21                                                                     (1 phr TBT)                                                                   Unmodified                                                                             435     1       NT    Fail  .06   45                                 Virgin                                                                        Vydyne 21                                                                     ______________________________________                                    

From the above table it can be seen that this TBT modification alsoimproves a virgin nylon.

Because Ti(OR)₄ compounds (where R is alkyl) have a tendency tohydrolyze in the presence of moisture, experiments were carried out toverify the hydrolytic stability of the nylon TBT dimer on wire.

Sample A is a standard nylon coated wire simply aged for nine days.

Sample B is a sample of TBT modified nylon wire over THEIC polyesterbase coat soaked in water for two hours.

Sample C is a sample of TBT modified nylon wire over THEIC polyesterwhere the wire was subjected to varying humidity -0 to 100% in 45 minuteintervals for five days at an average of 45° C.

    ______________________________________                                                 Sample A   Sample B Sample C                                         ______________________________________                                        Mandrel Pull                                                                             13           12       11                                                      13           13       13                                                      12           13       14                                           ______________________________________                                    

In a concurrent set of experiments TBT was added to a monoethanolamineequilibrated nylon enamel which contains a relatively large amount ofacetic acid. When this is done the following reaction occurs whichstrongly competes with dimer formation.

    CH.sub.3 COOH+Ti(OR).sub.4 →(CH.sub.3 COOH).sub.2 Ti(OR).sub.2

In order to determine what changes had been made to the nylon itself,modified and unmodified nylon enamels were run as sole coats.Essentially there was no change in general properties of the nyloncoating when TBT was added as a modifier.

The Tg and melt point of modified and unmodified nylons were comparedand found not to have been changed by the dimerization. This absence ofchange was to be expected. TBT treated nylon still passes the HCl acidblush test.

EXAMPLE 1

One part per hundred by weight of tetrabutyl titanate (TBT) was reactedwith nylon made from scrap nylon 6,6 fibers. A 5% by weight mixture ofthis modified nylon was made up with cresol, phenol, and/or xylene bymixing for one-half hour to form a homogeneous solution. This mixturewas coated on 18 AWG wire as described above. The change in propertieswere as shown in the table below.

    ______________________________________                                                          Mandrel Pull                                                        Df (250°)                                                                        Dry        Snap/Flex                                        ______________________________________                                        Enamel    0.05         1         Fail                                         Without TBT                                                                             0.16         7         Pass                                                   0.21        14         Pass                                         Same Enamel                                                                             0.05        12         Pass                                         With 3.5% TBT                                                                           0.14        12         Pass                                                   0.21        13         Pass                                         ______________________________________                                    

In this table Df values of between about 0.12 and about 0.28 represent acured enamel with values less than about 0.11 representing overcure. Inthe mandrel pull column, values greater than about 10 represent a"pass".

EXAMPLE 2

The same enamel as in Example 1 without TBT was run by coating an 18 AWGwire at a rate of speed of 45 feet per minute. Its runnability was sopoor that it could not be tested. This same enamel was tested with 3.5%TBT. The results are as shown below:

    ______________________________________                                                         Mandrel    Heat    Snap/                                              Df (250°)                                                                      Pull Dry   Shock   Flex                                      ______________________________________                                        Same enamel                                                                              Unuseable                                                          With 3.5% TBT                                                                            0.04      10         Pass  Pass                                               0.14      13         Pass  Pass                                               0.20      14         Pass  Pass                                    ______________________________________                                    

EXAMPLE 3

An enamel is made up using general purpose nylon Vydyne 21 from Monsantoand compared to the same enamel with 1% tetrabutyl titanate. The resultsare as shown below:

    ______________________________________                                                                Mandrel                                                        Df (250°)                                                                     Tg      Pull Dry  Snap/Flex                                   ______________________________________                                        Vydyne 21  .06      435      1      Fail                                                 .04      432      1      Fail                                                 .07      425     14      Pass                                      Vydyne 21  .06      435     10      Pass                                      With 1% TBT                                                                   ______________________________________                                    

The higher the Tg the greater the degree of cure. For example, values of425 are within the cure range whereas values of 435 are above the normalcure range.

EXAMPLE 4

A series of nylon enamels were made using amounts of tetrabutyl titanatevarying from 0.05 to 3.5%. Use of 0.05 and 0.1% parts per hundred didimprove the runnability of the nylon enamel (bead free). However, use of0.5% and 1% did show the same dramatic effect produced by the 3.5%level.

As stated above besides providing improved sole coats and topcoats forvarious polymer constructions, the modified nylon according to thepresent invention also produces an improved intermediate layer (bondcoat) in multiple layer constructions.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

I claim:
 1. A method of coating a magnet wire substrate comprisingapplying to an electrically conductive wire substrate at least one layerof an enamel composition comprising nylon reacted with 0.5% to 3.5% byweight based on the weight of the nylon present in the enamelcomposition of a tetraalkyl titanate.
 2. The method of claim 1 whereinthe titanate is selected from the group consisting of tetrabutyltitanate, tetrakis (2-ethylhexyl) titanate and tetraisopropyl titanate.3. The method of claim 1 further comprising applying a layer ofpolyester to said electrically conductive wire substrate prior toapplication of said nylon.
 4. The method of claim 1 further comprisingapplying a layer of polyurethane on said electrically conductive wiresubstrate prior to applying said nylon layer and applying a layer ofpolyvinyl butyral over said nylon layer.